Dean stayed still in the same place for a couple of seconds. He didn't know what kind of dangers were waiting for him if he crossed that tunnel and entered that place. Anyway, he couldn't back away anymore.
'I don't know the Dread that is hiding there. I am not as good as Rick or Clay to recognize Dreads just by their noise and their "Chaos". But, whatever is living after the end of this tunnel, it is perceptive enough to have perceived me from far away. Such high quantities of energy wouldn't pass unnoticed by me, I don't suck this much when feeling "Chaos" or "Willpower" in the environment. They were hiding their presence a long time ago...'
Those Dreads surely had high senses. They were probably tracking Dean's smell or noises from minutes ago.